Microsoft WSL Ubuntu 18.04 has recently released an upgrade that does not work for WSL. I came across this: "a fix has been made in Ubuntu Cosmic that should filter down to Bionic (18.04)"

The term "filter down" in association with "upgrade" has me perplexed. Wikipedia and other sources are too vague for me to understand. Can someone dumb it down for me?


Bugfixes in the pre-release version of Ubuntu (currently 18.10) are generally included in the release. That's a normal part of the cycle of creating a release that we like to call "testing".

Not all bugfixes get backported to older releases of Ubuntu (currently 18.04 and older). Those bugfixes must go through one of three processes to ensure quality. One of these processes is what "trickle down" refers to, since any of the three can take rather some time:


Filter down or trickle down refers to something moving from a higher point in the chain to a lower one. The fix is currently in Cosmic (18.10), which is the release after Bionic (18.04). However, since a forwards-compatible fix is available, they will now be able to back-port it to Bionic (18.04)

The benefits of this are that fixes can be tested in as-of-yet unreleased versions, and only the tested, stable versions of those fixes make it to the LTS release. This should help keep LTS releases bug-free.

  • Thank you for your answer. How do I command Ubuntu to stop trying to install this? Or should I just not worry about it? – lionheart Jun 3 '18 at 21:49

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